1. Field of the Invention
The present invention generally relates to a sheet feeding device, and more particularly, to an image reading device such as a scanner including a sheet feeding device and an image forming apparatus such as a copier or a facsimile incorporating the image reading device.
2. Description of the Background Art
Typically, an automatic document feeder (ADF) has a sheet feeding mechanism that is equipped with a sheet restriction member, also known as a shutter member, to stop a sheet stack consisting of multiple sheets at a predetermined position in order to prevent a user from placing an excess number of sheets at the far end in a sheet separating portion of the ADF where a single sheet is separated and fed to an image reading device one sheet at a time.
In one related-art sheet feeding mechanism, a sheet feed member is provided substantially at the upper portion of a document table on which a document to be read is placed. When reading a multi-sheet document placed on the document table, the sheet feed member, which is contactable to and separable from the sheets, feeds the sheets of the document to a separation portion of the ADF where the sheets are separated and fed to a downstream image reading device one sheet at a time.
The sheet feed mechanism also has a link member that causes the sheet restriction member, which is provided between the separation portion and the sheet feed member, to restrict advancement of the sheet. When the sheet is fed onward, the link member retracts the restriction member to a position at which the restriction member allows the sheet to move onward in conjunction with the sheet feed member contacting the sheet.
By contrast, as the sheet feed member separates from the sheet after feeding the sheet onward, the link member moves the sheet restriction member to a sheet restriction position to prevent the next sheet placed on the document table from advancing to the separation portion before the sheet feed member is ready to send the sheet.
Although generally adequate for its intended purpose, the above-described configuration has a drawback in that, because the restriction member is provided to an openably closable cover, the stacked sheets on the document table get disorganized when the cover is opened. Furthermore, this configuration does not have a release mechanism that releases stress applied to the sheet restriction member when a large number of sheets is fed and pushes the sheet restriction member, overstressing the sheet restriction member and thereby possibly damaging the sheet restriction member.
In another related-art sheet feeding mechanism, the sheet restriction member that aligns the leading edges of the sheets is rotatable about a shaft separate from a rotary shaft of a pick-up roller that contacts and picks up the sheet. The sheet restriction member includes a groove which the raised rotary shaft of the pick-up roller engages. When the pick-up roller is raised, the rotary shaft thereof engages the groove of the sheet restriction member, thereby regulating movement of the sheet restriction member. When the pick-up roller is lowered, the rotary shaft is released from the groove and can move freely.
Although advantageous, there is a drawback to such a configuration in that this configuration also does not include a system that releases stress applied to the sheet restriction member. Consequently, the restriction member may be damaged.
Furthermore, this configuration does not include an amplification mechanism for amplifying movement of the pick-up roller. Insufficient movement of the pick-up roller can cause the rotary shaft to remain in the groove.
Still further, the rotary shaft of the sheet restriction member needs to be disposed substantially above the pick-up roller so that the rotary shaft can engage the groove, thereby complicating efforts to make the device compact. If the rotary shaft of the sheet restriction member is not located substantially above the pick-up roller, desirable moment of rotation of the restriction member is difficult to achieve.
Still another related-art sheet feeding mechanism also includes a rotatable shutter member serving as the sheet-regulating restriction member that moves reciprocally up and down downstream from the sheet tray in a direction of conveyance of the sheet in conjunction with rotation of a rotary arm member provided above the sheet tray, the shutter member being rotatable about a rotary axis provided on a tip of the rotary arm member.
This configuration has a similar problem as in the foregoing related-art configurations in that this configuration also does not have a release mechanism that releases stress when the shutter member is overstressed. Consequently, the restriction member may be damaged. Furthermore, the need for space for the shutter member to move up and down complicates efforts to make the image forming apparatus compact.